Apparatus for forming flattened tubes with constant radii edge sections



Oct. 1, 1968 J. B. GREGOR ETAL 3,403,543

APPARATUS FOR FORMING ATTENED TUBES I WITH CONSTANT RADII EDGE SECTIONS Filed March 29, 1966 J INVENT OR 33 in JOHN B. GREGORY ARTHUR r. MCCLINTON PATRICK A. Wg/TT ING TON ATTORNEY United States Patent 3,403,543 APPARATUS FGR FORMING FLATTENED TUBES WITH CONSTANT RADII EDGE SECTIONS John B. Gregory, Accokeek, Md., Arthur T. McClinton, Arlington, Va., and Patrick A. Whittington, Forest Heights, Md., assignors to the United States of America as represented by the Secretary of the Navy Filed Mar. 29, 1966, Ser. No. 538,925

4 Claims. (Cl. 72-398) ABSTRACT OF THE DISCLOSURE A device for cold pressing metal tube stock to form flattened tubing having a constant radius of curvature of the edge sections which join the flattened walls. The device includes a pair of opposed dies to compress and flatten the tube and a pair of cylindrical mandrels which are insertable Within the tube and maintained in continuous engagement with the edge sections by a wedge.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to the metal forming art and, more particularly, to a means for cold pressing metal tube stock to form flattened tubing with constant ra'dii edge sections.

It has long been known that flattened tubing could be formed by cold pressing metal stock. However, the prior art methods of and means for so forming flattened tubing have all produced egging of the edge sections and, thus, have not been satisfactory when it is required that the flattened tubing have truly rounded edge sections such as, for example, if the tubing is to be used as a compliant tube reflector in an underwater acoustic transducer array.

The desirability of having the edge sections of a compliant tube reflector truly rounded or, in other words, having constant radii, is apparent when it is observed that such tubes are subjected to a vibrational environment and that failure thereof generally occurs at the point of greatest vibrational stress. Since the vibrational stress level at any point on the tube is approximately proportional to the radius of the curvature of the tube at that point, the egging of an edge section of the tube produces an edge section with an equivalent radius equal to the minimum radius of the egged portion thereof. Similar reasons dictate the requirement of constant radii edge sections when the flattened tubing is to be used in any other environment where it will be subjected to any other form of mechanical stress.

Accordingly, in contradistinction to the prior art, the general purpose of this invention is to provide a means for cold pressing metal tube stock to form flattened tubing with constant radii edge sections. To obtain this, the present invention contemplates, in generalized terms: inserting first and second mandrels longitudinally within the tube, each of the mandrels having a length at least equal to the length of the stock and a transverse cross-section which is constant along the length thereof and which has a circumference with a section of constant radius of curvature; applying compressive forces to opposed exterior sides of the stock to thereby flatten it; and maintaining an increasing portion of the constant radius of curvature sec- 3,403,543 Patented Oct. 1, 1968 tion of the circumference of each of the mandrels in firm engagement with a respective opposed interior side of the stock, the opposed interior sides being between the aforementioned opposed exterior sides thereof.

An object of the present invention is to provide ap paratus for use in cold pressing metal tube stock to form flattened tubing with constant radii edge sections.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood .by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 illustrates a transverse cross-section of the stock and apparatus of the present invention immediately after the mandrels and wedges have been inserted in the stock;

FIG. 2, which is taken along line 22 of FIG. 3 looking in the direction of the arrows, shows the transverse cross-section of the stock and apparatus of the present invention after the stock has been completely flattened; and

FIG. 3 illustrates a longitudinal cross-section of the completely flattened stock and apparatus of the present invention.

Referring to FIG. 1, it should be understood that the respective transverse cross-sections of stock 11, dies 12 and 13, and mandrels 16 and 17 are constant along their respective lengths. It should also be understood that, though stock 11 is shown as having an elliptical transverse cross-section, the preferred practice is to start by pressing stock having a circular transverse cross-section until it attains an elliptical transverse cross-section before proceeding in accordance with the present invention which is hereinafter described in detail.

Turning now to the details of FIG. 1, stock 11 is inserted between the upper and lower dies, 12 and 13 respectively, of a press indicated generally by 14. Dies 12 and 13 have respective lengths which are at least equal to the length of the stock. For purposes that are described hereinafter, dies 12 and 13 both have transverse cross-sections with convex, composite curves. The convex, composite curve portion of die 12 consists of end sections 21 and 22 having respective relatively small radii of curvature joined at respective points of transistion 23 and 24 to a center section 25 having a relatively large radius of curvature. The convex, composite curve portion of die 13 consists of end sections 26 and 27 having respective relatively small radii of curvature joined at respective points of transistion 28 and 29 to a center section 30 having a relatively large radius curvature. Stock 11 is placed between dies 12 and 13 so that the composite curves of the respective dies are both symmetrical about a first plane which extends the length of the stock and includes the minor axis aa of the ellipitical cross-section and, also, the longitudinal axis cc (FIG. 3) of stock 11.

Mandrels 16 and 17 each have transverse cross-sections enclosed by a circumference with a section of more than which has a constant radius of curvature. Preferably, mandrels 16 and 17 have circular transverse crosssections with grooves cut therein for receiving wedges 33 and 34 to thereby provide a firm engagement between the wedges and mandrels and to prevent rotation of the mandrels.

Mandrels 16 and 17 are inserted longitudinally within stock 11, preferably after being greased with graphite or the like. The wedges 33 and 34, after, preferably having also been greased with graphite or the like, are driven between mandrels 16 and 17 from opposite ends of stock 11 to force portions of the constant radius of curvature sections of the respective circumferences of mandrels 16 and 17 into firm engagement with opposite interior sides of stock 11. The combination of mandrels 16 and 17 and wedges 33 and 34 are so oriented within stock 11 that the portions of the constant radius of curvature sections of the respective circumferences of mandrels 16 and 17 which are in engagement with the opposed interior sides of stock 11 are symmetrical about a second plane which is orthogonal to the aforementioned first plane and which includes the major axis bb of the elliptical cross-section and, also, the longitudinal axis cc (FIG. 3) of stock 11.

After wedges 33 and 34 are inserted, dies 12 and 13 begin to apply compressive force to stock 11. This compressive force may be created by movement of one or both of dies 12 and 13. In fact, it is preferable that die 13 be fixed and that only die 12 move.

As the compressive force flattens stock 11, wedges 33 and 34 are driven in further (as better shown in FIG. 3), either manually or automatically, to maintain the portions of the constant radius of curvature sections of the respective circumferences of mandrels 16 and 17 in firm engagement with the opposite interior sides of stock 11. Of course, as stock 11 is flattened, these portions increase; but, they maintain their symmetry about the aforementioned second plane.

During the flattening of stock 11, a point is finally reached where the forces applied by wedges 33 and 34 on mandrels 16 and 17 are insufficient to overcome the forces applied thereon by tube stock 11 which latter mentioned forces tend to force mandrels 16 and 17 away from stock 11. If no additional forces were applied to mandrels 16 and 17 before this point was reached, flattening of tube stock 11 past this point would result in the undesired egging of the radii of the edge sections. This is the reason why dies 12 and 13 are provided with transistion points 23, 24 and 28, 29 respectively.

When transistion points 23 and 28 are brought into engagement with stock 11, an additional force is applied to mandrel 16 and this additional force is sufficient, in combination with the forces supplied by wedges 33 and 34, to overcome the force applied to mandrel 16 by tube stock 11. Likewise, when transistion points 24 and 29 are brought into engagement with stock 11, a like additional force is applied to mandrel 17. The proper radius of the curvature of the end sections 21, 22, 26, and 27 and of the center sections and 30 and the proper position of the transistions 23, 24, 28, and 29 to attain the necessary additional forces can be determined mathematically or experimentally.

Press 14 may be supplied with sides and 36 to aid in preventing tube stock 11 from bending away from mandrels 16 and 17. Sides 35 and 36 have respective inner faces 37 and 38 which are parallel to the aforementioned first plane and which are spaced apart a distance equal to the desired distance between the respective outer surface mid-points of the opposed rounded edge sections of the completely flattened tube as better shown in FIG. 2. In practice, sides 35 and 36 may be affixed to either of dies 12 and 13 and slidably engage the other of dies 12 and 13 and in this manner not only aid in preventing tube stock 11 from bending away from mandrels 16 and 17, but, also, aid in maintaining dies 12 and 13 in alignment.

FIG. 2, which illustrates a transverse cross-section of the completely flattened tube stock 11 and the combination according to the present invention of dies 12 and 13, mandrels 16 and 17, and wedges 33 and 34, shows that the flattened tubing 11 has dished faces and that the opposed rounded edge sections of constant radii have more than of arc. These facts follow from the particular shapes of and interrelations between dies 12 and 13, mandrels 16 and 17, and Wedges 33 and 34 which provide the desired flattened tubing with constant radii edge sections and which have been above described in detail.

FIG. 3, which illustrates a longitudinal cross-section of the flattened tube, mandrels 16 and 17, wedges 33 and 34, and sides 35 and 36, is primarily useful in appreciating the shape of wedges 33 and 34 and how these wedges are driven in from opposite sides of stock 11 as stock 11 is flattened.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. Configuring means for compressing metal tube stock into flattened tubing, said stock having a longitudinal axis and being symmetrical about each of first and second orthogonal planes both of which include said axis, said tubing having a transverse cross-section which is constant along the length thereof and which is defined by opposed faces joined by opposed edge sections having respective constant radii; said configuring means comprising:

first and second mandrels disposed within said stock,

each of said mandrels having a length at least equal to the length of said stock, a diameter which is constant along the length thereof and is less than /2 the diameter of said stock in said second plane, and a circumference of more than 180 and which is con stant along the length thereof, a section of said circumference having a constant radius of curvature; compression means disposed on each of opposed exterior sides of said stock to apply compressive forces to each of said exterior sides to thereby flatten said stock, the compressive forces applied to each of said exterior sides being symmetrical about said first plane and constant in any plane parallel to said first plane; said compression means includes first and second dies respectively disposed on said exterior sides; each of said dies being symmetrical about said first plane, having a length at least equal to the length of said stock, and having a transverse cross-section which is constant along the length thereof;

the transverse cross-section of each of said dies having end sections with respective relatively small radii of curvature joined by a center section with a relatively large radius of curvature; and

means for maintaining a portion of the control radius of curvature section of the circumference of each of said first and second mandrels in firm engagement with a respective one of opposed interior sides of said stock throughout the flattening thereof, each of said portions being symmetrical about said second plane and increasing as said stock is flattened;

whereby said dies aid in maintaining a portion of the constant radius of curvature section of the circumference of each of said first and second mandrels in firm engagement with a respective one of said interior sides of said stock throughout the flattening thereof.

2. The configuring means of claim 1 wherein the lengths of the respective chords extensible between the most mutually remote points on the center sections of the respective dies are both less than the internal width of said tubing in said second plane when said stock is completely flattened minus the sum of the diameters of said mandrels.

3. The configuring means of claim 1 wherein said Seeond'die has side sections aflixed thereto, said side sections having interior faces extending toward said first die in respective planes parallel to said first plane.

5 6 4. The configuring means of claim 1 wherein said References Cited means for maintaining a portion of the constant radius UNITED STATES PATENTS of curvature section of the circumference of each of said first and second mandrels in firm engagement with a respective one of said interior sides of said stock throughout 5 the flattening thereof includes wedges means and wherein each of said mandrels has a slot therein extending longi- CHARLES LANHAM Examine" tudinally thereof for receiving said wedge means. E. SUTTON, Assistant Examiner. 

